I saved this from somewhere ; maybe someone here a while ago.
See the comment re condensates and short trips.
"The electrical material properties of the engine oil change as the engine oil wears and ages. The changed electrical properties of the engine oil (dielectrics) cause the capacity of the capacitor to change.
The electronic evaluation unit converts the measured capacity into a digital signal. The digital sensor signal is sent to the engine management system. The engine management system uses the signal for internal calculations"
How the oil condition sensor works. In summary, it measures the conductivity of the oil. as the oil moves from base to acid, and contaminants collect in the oil, the oil becomes more conductive. The oil condition sensors monitors the change, and indicates the oil needs changed when the contaminants and acidity reach a certain threshold.
From the BMW System functions
The following system functions are described for the oil condition sensor:
! Measuring method
! Electronic oil level control
Measuring method
The oil condition sensor consists of 2 cylindrical condensers. The condensers are mounted above one another. 2 metal tubes are inserted one into the other to serve as electrodes. The engine oil is used as a dielectric medium between the electrodes.
Note! Explanation of the terms 'dielectric' and 'permittivity'.
A dielectric is defined as a non-conductive material in an electrical field. The electrical field is split by an insulator.
The permittivity (Latin: permittere = permit, let through) is also referred to as the dielectric conductance. The permittivity specifies the degree to which materials allow electrical fields to pass.
The factor indicates by how much the voltage at a capacitor drops when a dielectric, non-conducting material.
The temperature sensor is seated on the housing of the oil condition sensor. The housing of the oil condition sensor contains an electronic evaluation unit. The electronic evaluation unit has self-diagnosis. A fault in the oil condition sensor is entered in the fault memory of the engine management system.
The oil condition sensor sends its measured values to the engine management system:
! Engine oil temperature
! Oil level
! Engine oil quality
The electrical material properties of the engine oil change as the engine oil wears and ages. The changed electrical properties of the engine oil (dielectrics) cause the capacity of the capacitor to change. The electronic evaluation unit converts the measured capacity into a digital signal. The digital sensor signal is sent to the engine management system. The engine management system uses the signal for internal calculations (e.g. condensate in the engine oil).
Note: condensate in the engine oil.
Condensate that forms in the crankcase due to short distance driving can influence the permittivity. If the water is mixed in the engine oil, it also collects around the oil condition sensor.
If there is too much water in the crankcase:
In individual cases there can be an incorrect display of the oil level or a warning requesting that the oil be topped up.
This "false oil level warning" can be treated by means of a fault profile selection on the BMW diagnosis system, whereby the permittivity of the oil is also evaluated. However, there is no direct display of the permittivity. The permittivity depends on, among other things, the viscosity or age of the oil. This means that an appraisal of the quality is not ensured in every case. "